Microstructural Evolution and Mechanical Performance of Ambient-Cured Fly Ash–Metakaolin Inorganic Polymer Composites Activated by Anhydrous Sodium Silicate Powder

Notice

This is an unedited manuscript accepted for publication and provided as an Article in Press for early access at the author’s request. The article will undergo copyediting, typesetting, and galley proof review before final publication. Please be aware that errors may be identified during production that could affect the content. All legal disclaimers of the journal apply.

Year : 2026 | Volume : 14 | 04 | Page :
By

Ishant Dahat,

Bhushan H. Shinde,

  1. Research Scholar, Department of civil Engineering, G H Raisoni University, Amravati, Maharashtra, India
  2. Associate Professor, Department of civil Engineering, G H Raisoni University, Amravati, Maharashtra, India

Abstract

Inorganic geopolymer networks offer a low-carbon and sustainable solution to traditional binder systems through the alkali-activation of industrials-grade aluminosilicate material. The present paper focuses on the microstructure development and the mechanical performance of the ambient-cured fly ash – metakaolin inorganic polymer composite activated with solid anhydrous sodium silicate powder. Five inorganic polymer binder combinations were formulated by replacing fly ash with metakaolin at mass fractions of 0%, 10%, 20%, 30%, and 40%, respectively, while keeping the binder dosage and activator dosage constant, with a constant liquid to solid ratio. The developed binder mixture was then subjected to ambient curing without traditional heat curing to test their feasibility for practical and sustainable construction applications. Mechanical performance was characterized by compressive, flexural, and double shear strengths at various curing ages, while microstructure development and phase characterization were studied using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. Results suggested that incorporating metakaolin significantly affects geopolymerisation and leads to the formation of a more dense inorganic polymer matrix. Out of the five formulations considered, FA70MK30 (70% fly ash and 30% metakaolin) displayed the best overall mechanical performance with a maximum compressive strength of 38.67 MPa, flexural strength of 7.20 MPa, and double shear strength of 17.20 MPa. XRD results indicated better synthesis of amorphous sodium aluminosilicate hydrate (N-A-S-H) gel, while SEM images showed a relatively dense and less pore-holding microstructure with less unreacted material and finer structure altogether.

Keywords: Inorganic polymers, Fly ash, Metakaolin, Green composites, Microstructural characterization, Ambient curing, Mechanical properties.

How to cite this article: Ishant Dahat, Bhushan H. Shinde. Microstructural Evolution and Mechanical Performance of Ambient-Cured Fly Ash–Metakaolin Inorganic Polymer Composites Activated by Anhydrous Sodium Silicate Powder. Journal of Polymer & Composites. 2026; 14(04):-.
How to cite this URL: Ishant Dahat, Bhushan H. Shinde. Microstructural Evolution and Mechanical Performance of Ambient-Cured Fly Ash–Metakaolin Inorganic Polymer Composites Activated by Anhydrous Sodium Silicate Powder. Journal of Polymer & Composites. 2026; 14(04):-. Available from: https://journals.stmjournals.com/jopc/article=2026/view=256674

References

  1. Ghafoor MT, Khan QS, Qazi AU, Sheikh MN, Hadi MNS. Influence of alkaline activators on the mechanical properties of fly ash based geopolymer concrete cured at ambient temperature. Constr Build Mater. 2021;273:121752.
  2. Bhardwaj P, Gupta R, Salammal ST, Dhand C, Mishra D. Recent trends in mechanochemical processing of fly ash aluminosilicate materials (geopolymers): advancement, challenges, and opportunities. J Mater Cycles Waste Manag. 2024;26(1):1-19. doi:10.1007/s10163-023-01817-2
  3. Sankar K, Stynoski P, Al-Chaar GK, Kriven WM. Sodium silicate activated slag-fly ash binders: Part I – processing, microstructure, and mechanical properties. J Am Ceram Soc. 2018;101(6):2228-2244. doi:10.1111/jace.15391.
  4. Kaur M. Study on microstructure and pozzolonic properties of fly ash-based geopolymer mortar containing nano-metakaolin [PhD thesis]. Ludhiana: Punjab Agricultural University; 2018. Available from: https://krishikosh.egranth.ac.in/server/api/core/bitstreams/521aedbf-76dc-4a4b-ad5b-3c667f433c7c/content
  5. Masi G, Filipponi A, Bignozzi MC. Fly ash-based one-part alkali activated mortars cured at room temperature: effect of precursor pre-treatments. Open Ceram. 2021;8:100178.
  6. Qader DN, Jamil AS, Bahrami A, Ali M, Arunachalam KP. A systematic review of metakaolin-based alkali-activated and geopolymer concrete: a step toward green concrete. Rev Adv Mater Sci. 2025;64(1):20240076. doi:10.1515/rams-2024-0076.
  7. Alrefaei Y. Fresh and hardened properties of ambient cured one-part alkali-activated pastes along with superplasticizers [thesis]. Hong Kong: The Hong Kong Polytechnic University; 2021. Available from: https://theses.lib.polyu.edu.hk/handle/200/11235
  8. Wong V, Jervis W, Fishburn B, et al. Long-term strength evolution in ambient-cured solid-activator geopolymer compositions. Minerals. 2021;11(2):143.
  9. Nematollahi B, Sanjayan J, Shaikh FUA. Synthesis of heat and ambient cured one-part geopolymer mixes with different grades of sodium silicate. Ceram Int. 2015;41(4):5696-5704.
  10. Ukritnukun S. Development of ambient-cured low-alkali high-strength geopolymers [PhD thesis]. Sydney: University of New South Wales; 2017. Available from: https://unsworks.unsw.edu.au/bitstreams/62b3dd73-21ee-4236-be37-c549af6bceeb/download
  11. Singh A, Baghel SS, Bhadauria SS, Chaudhary S. Mechanochemical treatment of low-alkali activated slag concrete: a comparative study of potassium and sodium activators. J Mater Civ Eng. 2025;37(11):04025409. doi:10.1061/JMCEE7.MTENG-20467.
  12. Hamisi H. Synthesis of high-strength and durable metakaolin-based geopolymer cured at ambient temperature [PhD thesis]. Arusha: Nelson Mandela African Institution of Science and Technology; 2025.
  13. Sun D, Lee J, Mohyeddin A, Migunthanna J. Mechanical properties and reproducibility of one-part ambient-cured slag and fly ash-based geopolymer concrete. Buildings. 2026;16(4):707.
  14. Sood D, Hossain KMA. Strength, fracture and durability characteristics of ambient cured alkali-activated mortars incorporating high calcium industrial wastes and powdered reagents. Crystals. 2021;11(10):1167.
  15. Zerzouri M, Hamzaoui R, Ziyani L, Alehyen S. Comparative study of the structural, microstructural, and mechanical properties of geopolymer pastes obtained from ready-to-use metakaolin-quicklime powders and classic geopolymers. Materials. 2024;17(16):4151.
  16. Rakhimova N, Shi C. Factors affecting the performance of fly ash-slag geopolymers. J Mater Civ Eng. 2026;38(7):03126003. doi:10.1061/JMCEE7.MTENG-20952.
  17. Kanaan D, Safhi AEM, Suleiman AR, Soliman AM. Fresh, hardened, and microstructural properties of ambient cured one-part alkali-activated self-consolidating concrete. Sustainability. 2023;15(3):2451.
  18. Elhag AB, Raza A, Khan QUZ, et al. A critical review on mechanical, durability, and microstructural properties of industrial by-product-based geopolymer composites. Rev Adv Mater Sci. 2023;62(1):20220306. doi:10.1515/rams-2022-0306.
  19. Oti J, Adeleke BO, Anowie FX, Kinuthia JM, Ekwulo E. Mechanical properties of a sustainable low-carbon geopolymer concrete using a pumice-derived sodium silicate solution. Materials. 2024;17(8):1792.
  20. Wardhono A. The durability of fly ash geopolymer and alkali-activated slag concretes [PhD thesis]. Melbourne: RMIT University; 2024. Available from: https://research-repository.rmit.edu.au/articles/thesis/The_durability_of_fly_ash_geopolymer_and_alkali-activated_slag_concretes/27602319
  21. Hashem FS, Fadel O, Hassan HS, Selim FA. A comparative analysis of the effects of green blended activators on the durability and mechanical performance of slag-based geopolymer cement. Sci Rep. 2026;16(1):12752.
  22. Tennakoon CK. Assessment of properties of ambient cured geopolymer concrete for construction applications [PhD thesis]. Melbourne: Swinburne University of Technology; 2016. Available from: https://figshare.swinburne.edu.au/articles/thesis/Assessment_of_properties_of_ambient_cured_geopolymer_concrete_for_construction_applications/26294851
  23. Khater HM, ElMoied SA. Preparation and characterization of self-cured geopolymer binder using metakaolin precursor. Sci Rep. 2026;16(1):3270.
  24. Chen KY, Wang YQ, Min WL, et al. Performance characteristics of micro fiber-reinforced ambient cured one-part geopolymer mortar for repairing. Constr Build Mater. 2024;415:135086.
  25. Longhi MA, Rodriguez ED, Walkley B, et al. Metakaolin-based geopolymers: efflorescence and its effect on microstructure and mechanical properties. Ceram Int. 2022;48(2):2212-2229.
  26. Lv Y, Wang C, Han W, Li X, Peng H. Study of the mechanical properties and microstructure of alkali-activated fly ash-slag composite cementitious materials. Polymers. 2023;15(8):1903.
  27. Askarian M, Tao Z, Adam G, Samali B. Mechanical properties of ambient cured one-part hybrid OPC-geopolymer concrete. Constr Build Mater. 2018;186:330-337.
  28. Zhang Z, Bu Y, Guo S, et al. Optimization of additives for a metakaolin-fly ash-based geopolymer cementing slurry system at 70°C. SPE J. 2025;30(8):4627-4644.
  29. Assi LN, Deaver EE, Ziehl P. Using sucrose for improvement of initial and final setting times of silica fume-based activating solution of fly ash geopolymer concrete. Constr Build Mater. 2018;191:47-55.
Ahead of Print Subscription Original Research
Volume 14
04
Received 01/09/2026
Accepted 12/09/2026
Published 21/09/2026
Publication Time 20 Days

Login

My IP

PlumX Metrics

Support